This application relates to a refrigerant cycle utilizing tandem compressors sharing a common condenser, but having separate evaporators, and wherein an economizer circuit is employed.
Refrigerant cycles are utilized in applications to change the temperature and humidity or otherwise condition the environment. In a standard refrigerant system, a compressor delivers a compressed refrigerant to an outdoor heat exchanger, known as a condenser. From the condenser, the refrigerant passes through an expansion device, and then to an indoor heat exchanger, known as an evaporator. At the evaporator, moisture may be removed from the air, and the temperature of air blown over the evaporator coil is lowered. From the evaporator, the refrigerant returns to the compressor. Of course, basic refrigerant cycles are utilized in combination with many configuration variations and optional features. However, the above provides a brief understanding of the fundamental concept.
In more advanced refrigerant systems, a capacity of the air conditioning system can be controlled by the implementation of so-called tandem compressors. The tandem compressors are normally connected together via common suction and common discharge manifolds. From a single common evaporator, the refrigerant is returned through a suction manifold, and then distributed to each of the tandem compressors. From the individual compressors the refrigerant is delivered into a common discharge manifold and then into a common single condenser. The tandem compressors are also separately controlled and can be started and shut off independently of each other such that one or both compressors may be operated at a time. By controlling which compressor is running, control over the capacity of the combined system is achieved. Often, the two compressors are selected to have different sizes, such that even better of capacity control is provided. Also, tandem compressors may have shutoff valves to isolate some of the compressors from the active refrigerant circuit, when they are shutdown. Moreover, if these compressors operate at different suction pressures, then pressure equalization and oil equalization lines are frequently employed.
One advantage of the tandem compressor is that better capacity control is provided, without the requirement of having each of the compressors operating on a dedicated circuit. This reduces the system cost.
However, certain applications require cooling at various temperature levels. For example, in supermarkets, low temperature (refrigeration) cooling can be provided to a refrigeration case by one of the evaporators connected to one compressor and intermediate temperature (perishable) cooling can be supplied by another evaporator connected to another compressor. In another example, a computer room and a conventional room would also require cooling loads provided at different temperature levels, which can be supplied by the proposed multi-temp system as desired. However the cooling at different levels will not work with application of standard tandem compressor configuration, as it would require the application of a dedicated circuit for each cooling level. Each circuit in turn must be equipped with a dedicated compressor, dedicated evaporator, dedicated condenser, and dedicated evaporator and condenser fans. This arrangement having a dedicated circuitry for each temperature level would be very expensive.
In addition, a technique known as an economizer circuit has been utilized in the refrigerant systems. The economizer circuit increases the capacity and efficiency of a refrigerant cycle. To this point, a system having a common condenser communicating with several evaporators has not been utilized in combination with an economizer circuit. Notably, applicants have a co-pending application, filed on even date herewith, entitled “Refrigerant Cycle With Tandem Compressors for Multi-Level Cooling, and assigned Ser. No. 10/975,887.